Abstract T P225: cGMP-Dependent Protein Kinase I in Smooth Muscle Cells Protects Against Stroke Injury in Mice

The signaling pathways by which NO protects against stroke injury are mediated by cyclic guanosine monophosphate (cGMP) formation. However, the mechanisms of downstream signaling from cGMP to smooth muscle cells (SMC) remain incompletely understood. The cGMP-dependent protein kinase I (cGKI) is a key mediator of cGMP signaling. The goal of this study is to test the hypothesis that cGKI in SMC protects against stroke injury. Animals: We used the novel mouse line for highly efficient tamoxifen-inducible SMC-specific gene knockout, SMA-CreERT2, which expresses the CreERT2 recombinase under the control of the smooth muscle alpha-actin promoter (cGKI KO mice). The litter mate wild-type (WT) mice (no Cre gene) receiving the same tamoxifen treatment were used as control (cGKI WT) mice. Methods and Results: Mean blood pressure measured acutely from the common carotid artery under anesthesia (30% oxygen, 70% nitrous oxide and 1.5% isoflurane) was higher in cGKI KO mice (107±8 mmHg, Mean±SD) than in cGKI WT mice (95±1 mmHg, n=4/group, P<0.05). One hour of middle cerebral artery (MCA) occlusion by filament with 23 hours of reperfusion produced increased cerebral infarct volume (TTC staining, indirect calculation) in cGKI KO mice (123±39 mm3) as compared with cGKI WT (85±17 mm3, n=5/group, p< 0.05). Neurological deficit by 5 point scale was worse in cGKI KO mice (4.0 points) as compared with cGKI WT (2.4 points). Cerebral blood flow monitored by laser Doppler flowmetry above the core of the MCA territory indicated that reperfusion was less in cGKI KO mice than in cGKI WT mice, suggesting that cGKI mediates cerebrovascular SMC relaxation and protects against ischemic stroke. Vascular relaxation of mesenteric resistance arteries to acetylcholine, and the NO donor, NONOate after preconstriction with phenylephrine was dramatically impaired in cGKI KO mice. It suggests the importance of cGKI in the vascular SMC for NO-induced relaxation. In conclusion, stroke injury was more pronounced in cGKI SMC specific inducible conditional knockout mice than in cGKI WT mice, suggesting a protective role for cGKI in SMC against cerebral reperfusion injury. These studies identify the cGKI in cerebral vasculature as a potential target for therapies aimed at reducing stroke injury.